1. Fields of the Invention
The present invention relates to a roll screen control member, especially to a roll screen control member with a novel design that drives a roll screen tube to rotate precisely and further controls an extended or retracted state of a screen of the roll screen.
2. Descriptions of Related Art
The roll screen control member available now is composed of a sprocket wheel, a chain protection cover, a sprocket support, a cover spring, a splined bush and a central pin. The splined bush is mounted with a roll screen tube while the central pin includes a central pin head with a single cutting surface corresponding to a cutting surface on an inner wall of the sprocket support. After the central pin being locked into the sprocket support, they are locked and fixed with each other by matching and corresponding of the cutting surface of the central pin head with the cutting surface on the inner wall of the sprocket support.
However, in practice, such locking and fixing way by means of only a single cutting surface raises a problem. When the chain moves so as to make the cover spring drive the splined bush rotating the roll screen tube, a spin or slide occurs once a transmission torque exerted is too large and the fixing between the central pin and the sprocket support is not so securely. Especially when the size of the roll screen is getting larger, its transmission torque increases and the condition becomes more obvious.
Refer to U.S. Pat. No. 7,100,668, at least one fins is disposed on a center-pin head of a center pin while at least one recess is mounted in a sprocket support that is inserted by the center-pin head. The fin of the center pin is adapted to co-operatively engage with the recess in the sprocket support. The problem of spin or slide caused by unsecured fixing between the central pin and the sprocket support can be solved by the engagement between the fin and the recess.
A roll screen control member of the present invention can also prevent the spin or slide caused by unsecured fixing between the central pin and the sprocket support.